1. Field of the Invention
The invention relates to microprocessors, and more particularly, to a circuit for properly powering up a microprocessor in a computer system.
2. Description of the Related Art
Over the past several years, the performance of microprocessors has improved at a rapid rate. The different generations of the 80xc3x9786 processors from Intel Corporation provide an example of how the performances and capabilities of microprocessors have improved from one generation to the next. For example, the 80486 family of processors include many features that did not exist in the 80386 family of processors. The 80486 processor includes a local or internal cache memory, internal floating point unit, and other on-chip functions to provide for higher integration. The next generation of processors from Intel was the Pentium P5 family of processors, which contained several enhancements over the 80486 processors. These enhancements include an internal floating point unit which implemented faster algorithms, internal code and data caches, increased data bus width to improve data transfer rates, and bus cycle pipelining. In addition, the P5 processors are manufactured with more advanced processing technology, which allows them to operate at higher frequencies than prior generation processors.
The most recent generation of microprocessors from Intel is the P6 family of processors. Among the enhancements offered by the P6 family of processors is an integrated second level cache in addition to the first level cache. This further improves computer system performance. In addition, using an integrated second level cache reduces the overall system board size as separate cache controllers and cache memory devices are not needed for a second level cache.
However, Intel""s P6 processor is not without its problems. At least one version of the P6 processor experiences problems when it is power cycled. If power is turned on to the P6 processor and then turned off for about 30 to 40 seconds, the P6 processor does not appear to come out of reset when power is again restored. Typically, power on a computer system board is cycled to test the behavior of the board. Because of the power-cycling problem experienced by the P6 processors, computer system board manufacturers are unable to test their boards properly.
It is therefore desired that a solution be identified to fix the power-up problem being experienced by the P6 processor.
To overcome the problem discussed above, a circuit according to the present invention generates a double-edged power-good indication signal to the P6 microprocessor in a computer system. After a power supply circuit indicates that the power supply voltages have stabilized and are within tolerance limits, the circuit according to the present invention asserts the power-good indication signal. A first predetermined period later, the power-good indication signal is deasserted. The power-good indication signal remains deasserted for a second predetermined period. Next, the power-good indication signal is reasserted and is maintained asserted until the power supply circuit removes its indication that the power supply voltages are stable and within threshold levels. The two rising edges of the power-good indication signal allows the P6 microprocessor to power up properly after it is power cycled.